ext/bcmath: Prevent overflow of uint32_t/uint64_t (php#14297)

If add more than a certain number of times, it will overflow, so need to adjust
the digits before adding.

Author: SakiTakamachi

ext/bcmath/libbcmath/src/recmul.c

@@ -39,15 +39,25 @@
 
 #if SIZEOF_SIZE_T >= 8
 #  define BC_MUL_UINT_DIGITS 8
-#  define BC_MUL_UINT_OVERFLOW 100000000
+#  define BC_MUL_UINT_OVERFLOW (BC_UINT_T) 100000000
 #else
 #  define BC_MUL_UINT_DIGITS 4
-#  define BC_MUL_UINT_OVERFLOW 10000
+#  define BC_MUL_UINT_OVERFLOW (BC_UINT_T) 10000
 #endif
 
+#define BC_MUL_MAX_ADD_COUNT (~((BC_UINT_T) 0) / (BC_MUL_UINT_OVERFLOW * BC_MUL_UINT_OVERFLOW))
+
 
 /* Multiply utility routines */
 
+static inline void bc_digits_adjustment(BC_UINT_T *prod_uint, size_t prod_arr_size)
+{
+	for (size_t i = 0; i < prod_arr_size - 1; i++) {
+		prod_uint[i + 1] += prod_uint[i] / BC_MUL_UINT_OVERFLOW;
+		prod_uint[i] %= BC_MUL_UINT_OVERFLOW;
+	}
+}
+
 /*
  * Converts BCD to uint, going backwards from pointer n by the number of
  * characters specified by len.
@@ -141,7 +151,18 @@ static void bc_standard_mul(bc_num n1, size_t n1len, bc_num n2, size_t n2len, bc
 	bc_convert_to_uint(n2_uint, n2end, n2len);
 
 	/* Multiplication and addition */
+	size_t count = 0;
 	for (i = 0; i < n1_arr_size; i++) {
+		/*
+		 * This calculation adds the result multiple times to the array entries.
+		 * When multiplying large numbers of digits, there is a possibility of
+		 * overflow, so digit adjustment is performed beforehand.
+		 */
+		if (UNEXPECTED(count >= BC_MUL_MAX_ADD_COUNT)) {
+			bc_digits_adjustment(prod_uint, prod_arr_size);
+			count = 0;
+		}
+		count++;
 		for (size_t j = 0; j < n2_arr_size; j++) {
 			prod_uint[i + j] += n1_uint[i] * n2_uint[j];
 		}
@@ -151,10 +172,7 @@ static void bc_standard_mul(bc_num n1, size_t n1len, bc_num n2, size_t n2len, bc
 	 * Move a value exceeding 4/8 digits by carrying to the next digit.
 	 * However, the last digit does nothing.
 	 */
-	for (i = 0; i < prod_arr_size - 1; i++) {
-		prod_uint[i + 1] += prod_uint[i] / BC_MUL_UINT_OVERFLOW;
-		prod_uint[i] %= BC_MUL_UINT_OVERFLOW;
-	}
+	bc_digits_adjustment(prod_uint, prod_arr_size);
 
 	/* Convert to bc_num */
 	*prod = bc_new_num_nonzeroed(prodlen, 0);

ext/bcmath/tests/bcmul_check_overflow.phpt

@@ -0,0 +1,35 @@
+--TEST--
+bcmul() checking overflow
+--EXTENSIONS--
+bcmath
+--INI--
+bcmath.scale=0
+--FILE--
+<?php
+for ($i = 1; $i < 15; $i++) {
+    $repeat = 2 ** $i;
+    $num1 = str_repeat('99999999', $repeat);
+    /*
+     * 9999 * 9999 = 99980001
+     * 99999999 * 99999999 = 9999999800000001
+     */
+    $expected = str_repeat('9', $repeat * 8 - 1) . '8' . str_repeat('0', $repeat * 8 - 1) . '1';
+    $actual = bcmul($num1, $num1);
+    echo $repeat . ': ' . ($actual === $expected ? 'OK' : 'NG') . PHP_EOL;
+}
+?>
+--EXPECT--
+2: OK
+4: OK
+8: OK
+16: OK
+32: OK
+64: OK
+128: OK
+256: OK
+512: OK
+1024: OK
+2048: OK
+4096: OK
+8192: OK
+16384: OK